Physical,Chemical, and Biological Changes in the Rhizosphere and Nutrient Availability

The rhizosphere is the soil zone adjacent to plant roots which is physically, chemically, and biologically different from bulk or non-rhizosphere soil. Adaptative mechanisms of plants influence physical (temperature, water availability, and structure), chemical [pH, redox potential, nutrient concentration, root exudates, aluminum (Al) detoxification and allelopathy], and biological properties (microbial association) in the rhizosphere. These changes affect nutrient solubility, transport, and uptake and ultimately plant growth. Major rhizosphere changes are synthesized and their influence on nutrient availability is discussed. In the last decade, significant progress has been made in understanding the rhizosphere environment and nutrient availability. However, the subject matter is very complex and more research is needed to understand the interaction between the plant, the rhizosphere environment, and nutrient availability.     

Integrated Nutrient Management Affects Fruit Yield of Sapota (Achras zapota L.) and Nutrient Availability in a Vertisol

ABSTRACT

We studied the effect of integrated nutrient management (INM) combinations on supplement of plant nutrient for quantitative and qualitative fruit production in sapota. Thus, 17 combinations of INM practices were evaluated on fruit yield of sapota and nutrient availability in a Vertisol of Chambal region, India. The results demonstrated that almost all treatment combinations comprised of recommended dose of fertilizer (RDF), i.e. 1,000:500:500 g NPK plant^?1 with application of organic and inorganic sources of nutrients had a significant effect on the fruit yield of sapota, soil microbial biomass, NPK content of leaf, fruit and soil over control (T₁). Among different treatments, application of 2/3rd part of RDF + 50 kg FYM + 250 g Azospirillum + 250 g Azotobacter plant^?1 (T₁₁) significantly enhanced the number of fruits plant^?1 (327.88), yield plant^?1 (29.03 kg) and yield ha^?1 (4.52 t). However, the soil microbial count of fungi (8.89 cfu g^?1 soil), bacteria (11.19 cfu g^?1 soil) and actinomycetes (5.60 cfu g^?1 soil) at fruit harvest was higher under the 2/3 of RDF +10 kg vermicompost + 250 g Azospirillum + 250 g Azotobacter plant^?1 (T₁₅). The leaf nitrogen content (N, 2.03%) was higher in T_15, while phosphorus (P, 0.28%) and potassium (K, 1.80%) content were higher in T₁₁. It is evident that treatment T₁₁ increased fruit yield by 32% in Sapota cv. Kalipatti compared to control. Therefore, combined application of nutrient sources proved not only beneficial for enhancing fruit yield of sapota but also sustaining soil health in Chambal region of south-eastern Rajasthan.     

Root Growth,Nutrient Uptake,and Nutrient-Use Efficiency by Roots of Tropical Legume Cover Crops as Influenced by Phosphorus Fertilization

Roots are important organs that supply water and nutrients to growing plants. Data related to root growth and nutrient uptake by tropical legume cover crops are limited. The objective of this study was to evaluate root growth of tropical legume cover crops and nutrient uptake and use efficiency under different phosphorus (P) levels. The P levels used were 0 (low), 100 (medium), and 200 (high) mg kg^?1 of soil, and five cover crops were evaluated. Root dry weight, maximum root length, and specific root length were significantly influenced by P and cover crop treatments. Maximum values of these root growth parameters were achieved with the addition of 100 mg P kg^?1 soil. The P?×?cover crops interactions for all the macro- and micronutrients, except manganese (Mn), were significant, indicating variation in uptake pattern of these nutrients by cover crops with the variation in P rates. Overall, uptake pattern of macronutrients was in the order of nitrogen (N) > calcium (Ca) > potassium (K) > magnesium (Mg) > P and micronutrient uptake pattern was in the order of iron (Fe) > Mn > zinc (Zn) > copper (Cu). Cover crops which produced maximum root dry weight also accumulated greater amount of nutrients, including N, compared to cover crops, which produced lower root dry weight. Greater uptake of N compared to other nutrients by cover crops indicated that use of cover crops in the cropping systems could reduce loss of nitrate (NO₃ ^?) from soil–plant systems. Increase in root length and root dry weight with the addition of P can improve nutrient uptake from the soil and lessen loss of macro- and micronutrients from the soil–plant systems.     

Effects of Vesicular Arbuscular Mycorrhizae and Applied Phosphorus through Targeted Yield Precision Model on Root Morphology,Productivity, and Nutrient Dynamics in Soybean in an Acid Alfisol

A field experiment was conducted in a phosphorus (P)–deficient acidic Alfisol in northwestern Himalayas to study the effect of three vesicular arbuscular mycorrhizae (VAM) cultures [VAM_L, local VAM culture (Glomus mosseae) developed by CSK Himachal Pradesh Agricultural University, Palampur, India; VAM_T, VAM culture (Glomus intraradices) developed by Centre for Mycorrhizal Research, The Energy and Resources Institute (TERI), New Delhi, India; and VAM_I, VAM culture (Glomus mosseae) developed by Indian Agricultural Research Institute (IARI), New Delhi, India] on growth, productivity, and nutrient dynamics in rainfed soybean. Plant height, aboveground dry matter, root dry matter, total dry matter, root length, root weight density, Rhizobium root nodule count, root colonization, yield attributes, yield, and nutrient uptake of soybean increased consistently and significantly with increase in inorganic P levels from 25 to 75% of recommended P₂O₅ dose based on targeted yield precision model coupled with various VAM cultures. VAM_T (Glomus intraradices) at each P level showed its superiority over VAM_I and VAM_L. Sole application of any of the three VAM cultures produced similar growth and development parameters as well as grain yield (18.68 to 19.08 q ha^?1) as produced through farmers’ practice (nitrogen at 20 kg ha^?1), indicating that VAM has a vital role in root morphology and nutrient dynamics in a soil–plant system, though significantly greater productivity was obtained with 100% of the recommended P₂O₅ dose based on soil-test crop response (STCR) precision model without VAM inoculation. Targeted grain yield of soybean (25 q ha^?1) was achievable with 75% of the recommended P₂O₅ dose applied with any of the three VAM fungi cultures without impairing soil fertility, thereby indicating that VAM fungi can save about 25% P fertilizer in soybean in P-deficient acidic Alfisols of northwestern Himalayas.     

Selected Soil Enzyme Activities,Soil Microbial Biomass Carbon,and Root Yield as Influenced by Organic Production Systems in Sweet Potato

A field experiment was conducted on Typic Rhedustalfs to determine the effects of various organic production systems. Results revealed that the soil microbial biomass carbon (SMBC) content was greatest with the application of 100% N through farmyard manure. The ratio index value of biofertilizer along with 50% N through any one of the organic sources were greater than 100% N through green leaf manure?/?vermicompost, integrated use of manure and fertilizer (conventional production system), and control (traditional system of production). Soil enzymes varied with the production systems. The urease, phosphatase, and β-glucosidase activities were more with greater nitrogen, phosphorus, and organic-matter treatments, respectively. The SMBC, soil enzymes, and microbial activity were very responsive to organic production systems, but their levels and activities were not reflected in sweet potato root yield.     

Influence of Vesicular Arbuscular Mycorrhizal Fungi and Applied Phosphorus on Root Colonization in Wheat and Plant Nutrient Dynamics in a Phosphorus-Deficient Acid Alfisol of Western Himalayas

Vesicular arbuscular mycorrhizal (VAM) fungi symbiosis confers benefits directly to the host plant's growth and yield through acquisition of phosphorus and other macro- and micronutrients, especially from phosphorus (P)–deficient acidic soils. The inoculation of three VAM cultures [viz., local culture (Glomus mosseae), VAM culture from Indian Agricultural Research Institute (IARI), New Delhi (Glomus mosseae), and a culture from the Centre for Mycorrhizal Research, Energy Research Institute (TERI), New Delhi (Glomus intraradices)] along with P fertilization in wheat in a P-deficient acidic alfisol improved the root colonization by 16–24% while grain and straw yields increased by 12.6–15.7% and 13.4–15.4%, respectively, over the control. Uptake of nitrogen (N), P, potassium (K), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) was also improved with VAM inoculation over control, but the magnitude of uptake was significantly greater only in the cases of P, Fe, Zn, and Cu. Inoculation of wheat with three VAM cultures in combination with increasing inorganic P application from 50% to 75% of the recommended P₂O₅ dose to wheat through the targeted yield concept following the soil-test crop response (STCR) precision model resulted in consistent and significant improvement in grain and straw yield, macronutrient (NPK) uptake, and micronutrient (Fe, Mn, Zn, Cu) uptake in wheat though root colonization did not improve at P₂O₅ doses beyond 50% of the recommended dose. The VAM cultures alone or in combination with increasing P levels from 50% to 75% P₂O₅ dose resulted in reduction of diethylenetriaminepentaacetic acid (DTPA)–extractable micronutrient (Fe, Mn, Zn, Cu) contents in P-deficient acidic soil over the control and initial fertility status, although micronutrient contents were relatively greater in VAM-supplied plots alone or in combination with 50% to 75% P₂O₅ dose over sole application of 100% P₂O₅ dose, thereby indicating the positive role of VAM in nutrient mobilization and nutrient dynamics in the soil–plant system. There was significant improvement in available N and P status in soil with VAM inoculation coupled with increasing P levels upto 75% P₂O₅ dose, although the greatest P buildup was obtained with sole application of 100% P₂O₅ dose. The TERI VAM culture (Glomus intraradices) showed its superiority over the other two cultures (Glomus mosseae) in terms of crop yield and nutrient uptake in wheat though the differences were nonsignificant among the VAM cultures alone or at each P level. Overall, it was inferred that use of VA-mycorrhizal fungi is beneficial under low soil P or in low input (nutrient)–intensive agroecosystems.     

Root Exudates of Rice Cultivars Affect Rhizospheric Phosphorus Dynamics in Soils with Different Phosphorus Statuses

Exudation of organic acids by the roots of three rice cultivars grown in three soils of different phosphorus (P) statuses, and their impacts on the rhizospheric P dynamics and P uptake by the rice plants, were investigated. Quantum root exudates from all the rice cultivars were significantly greater at 21 days after transplantation than at panicle initiation or flowering stages. Malic acid was the most predominant organic acid present in the rice root exudates (10.3 to 89.5 μmol plant^?1 d^?1), followed by tartaric, citric, and acetic acids. Greater exudation of organic acids from rice grown in P-deficient soil by all the rice cultivars suggested response of rice plant to P stress. Results indicate that the release of organic acids in the root exudates of rice plants can extract P from strongly adsorbed soil P fraction, thereby increasing native soil P utilization efficiency and ensuring adequate P nutrition for the growing rice plants.     

免耕留茬覆盖对旱作燕麦土壤养分及微生物量的影响

以旱作燕麦田为试验对象,设置免耕高留茬高覆盖、免耕低留茬高覆盖、免耕高留茬低覆盖、免耕低留茬低覆盖和常规耕作5个处理,研究了免耕留茬覆盖对土壤养分、微生物量及燕麦产量的影响。结果表明,免耕留茬覆盖各处理均能明显提高土壤0—10cm和10—20cm土层中土壤有机质、全量养分及速效养分含量,0—10cm土层各土壤养分含量均高于10—20cm土层;免耕留茬覆盖对土壤微生物碳、氮具有显著的提高作用,整个生育期抽穗期达到最大值,0—10cm土层土壤微生物量碳、氮均大于10—20cm土层,其中免耕高留茬高覆盖处理效果最佳;免耕留茬覆盖对0—10cm和10—20cm土壤微生物商有显著提高作用,免耕留茬覆盖处理间差异不显著;免耕留茬覆盖对燕麦产量影响显著,其中高留茬高覆盖处理产量最高,为2 111.4kg/hm~2,较常规耕作增产18.6%,产量总体表现为免耕高留茬高覆盖免耕低留茬高覆盖免耕高留茬低覆盖免耕低留茬低覆盖常规耕作。     

Interrelationship of Carbon Sequestration,Soil Fertility,and Microbial Indices as Influenced by Long-Term Land Uses in Lower Himalayan Region,India

The study was conducted to determine the long-term impact of different land uses on carbon sequestration, soil fertility, and microbial indices and to establish their interrelationship in a light-textured hyperthermic Udic Ustochrept. Soil samples were collected from existing land-use systems of (1) Eucalyptus tereticornis, (2) Terminalia chebula, (3) Acacia nilotica, (4) Leucaena leucocephala, (5) Embilica officinalis, (6) Zizyphus spp., and (7) maize–wheat rotation from depths of 0–15, 15–30, and 30–45 cm and examined for pH; organic carbon (OC); electrical conductivity (EC); available nitrogen (N), phosphorus (P), and potassium (K); micronutrients; microbial biomass carbon (MBC); microbial biomass nitrogen (MBN); and microbial biomass phosphorus (MBP). High-density plantations of Eucalyptus teriticornis had a greater potential in sequestering aboveground carbon (472.37 Mg ha^?1), compared to widely spaced trees of Acacia nilotica (376.05 Mg ha^?1). Eucalyptus teriticornis exhibited the greatest impact in increasing soil OC in all depths, followed by Acaccia nilotica and Terminalia chebula, and the lowest was in agriculture (0.778, 0.749, 0.590, and 0.471%, respectively, in surface soil). Available zinc and iron contents were greatest under Eucalyptus tereticornis, followed by Acacia nilotica, Zizyphus mauritiana, Embilica officinalis, Terminalia chebula, and Leucaena leucocephala. The MBC and MBN were greatest in Eucalyptus tereticornis, followed by Acacia nilotica, and lowest in agriculture. Correlation matrix revealed significant and positive relationships between carbon sequestered with OC, MBC, MBN, and MBP.     

Yield,Nutrient Uptake,and Changes in Soil Chemical Properties as Influenced by Liming and Iron Application in Common Bean in a No-Tillage System

Soil acidity is the principal limiting factor in crop production in Oxisols, and deficiency of micronutrients has increased in recent years because of intensive cropping. A field experiment was conducted over three consecutive years to assess response of common bean (Phaseolus vulgaris L.) to lime and iron (Fe) applications on an Oxisol in a no-tillage system. Changes in selected soil chemical properties in the soil profile (0- to 10- and 10- to 20-cm depths) with liming were also determined. Lime rates used were 0, 12, and 24 Mg ha^–1, and Fe application rates were 0, 50, 100, 150 200, and 400 kg ha^–1. Both lime and Fe were applied as broadcast and incorporated in the soil. Grain yields of common bean were significantly increased with the application of lime. Iron application, however, did not influence bean yield. There were significant changes in soil profile (0- to 10-cm and 10- to 20-cm depths) in pH, calcium (Ca²⁺), magnesium (Mg²⁺), hydrogen + aluminum (H⁺ + Al³⁺), base saturation, acidity saturation, cation exchange capacity (CEC), Ca²⁺ saturation, Mg²⁺ saturation, potassium (K⁺) saturation, and ratios of Ca/Mg, Ca/K, and Mg/K. These soil chemical properties had significant positive association with common bean grain yield. Averaged across two depths and three crops, common bean produced maximum grain yield at pH_w 6.3, Ca²⁺ 3.8 cmol_c kg^–1, Mg²⁺ 1.1 cmol_c kg^–1, 3.5 H⁺ + Al³⁺ cmol_c kg^–1, acidity saturation 41.8%, CEC 7.5 cmol_c kg^–1, base saturation 57.4%, Ca saturation 45.2%, Mg saturation 14.2%, K saturation 9.1%, Ca/Mg ratio 3.1, Ca/K ratio 22.6, and Mg/K ratio 6.7.     

安徽省淮河流域湿地土壤养分流失及水质动态研究

以淮河流域(安徽段)湿地为研究区域,连续3a(2012—2014年)在野外调查和室内分析的基础上,采用定点实地调查、土壤和水质采样相结合的方法,研究了不同水期(平水期、丰水期和枯水期)淮河流域湿地土壤养分流失、水质动态及湿地植被多样性特征,并运用冗余分析(RDA)和偏相关分析手段揭示不同水期淮河流域湿地植被多样性与环境因子之间的关系。结果表明:(1)淮河流域湿地植被Shannon-Wiener多样性指数(H)、Pielou均匀度指数(J_P)、Margalef种类丰富度指数(d_(Ma))在丰水期达到最高,平水期和枯水期较低,基本表现为丰水期枯水期平水期,Simpson优势度指数(D)基本表现为平水期枯水期丰水期。(2)不同水期土壤pH、电导率、全盐和总孔隙度在0—40cm剖面上变化趋势基本一致,不同水期土壤pH随土层深度的增加而增加,电导率和全盐含量呈先降低后增加趋势,土壤总孔隙度呈降低趋势。(3)随着水期的变化,土壤DP、K~+、SEP和SEK呈增加趋势,在枯水期达到峰值,平水期最低,基本表现为枯水期丰水期平水期,土壤DP、K~+和SEK增加幅度逐渐增加,而土壤SEP增加幅度逐渐减小,以SEK含量波动较大。(4)水温、TN、TP、BOD5和CODCr呈一致的变化规律,随水期的变化呈先增加后降低趋势,透明度呈"V"字形变化规律,基本表现为平水期枯水期丰水期。(5)偏相关分析显示,不同水期淮河流域湿地植被多样性均与透明度呈极显著的负相关(P0.01),透明度能够反映出淮河湿地植被多样性及水质状况,影响平水期和枯水期植被多样性主要因子为BOD5浓度和CODCr浓度,影响丰水期植被多样性主要因子为TN浓度和TP浓度。     

Improvement in Productivity,Water-Use Efficiency,and Soil Nutrient Dynamics of Summer Peanut (Arachis hypogaea L.) through Use of Polythene Mulch,Hydrogel, and Nutrient Management

Agronomic management through better use of inputs benefits farmers both by enhancing productivity and profitability. A field experiment was conducted in consecutive summer seasons (2011–2013) consisting of two mulching (no mulch, polythene mulch), three hydrogel (0, 2.5, 5.0 kg ha^?1), and three nutrient management treatments (organic, inorganic, and integrated) in a split–split plot design. Use of mulching and 2.5 kg hydrogel ha^?1 and integrated nutrient management enhanced pod, haulm, kernel and oil yields, and net economic returns. Partial factor productivity and water-use efficiency were higher under polythene mulch and 5.0 kg hydrogel ha^?1. Higher nutrient uptakes were obtained under both mulching and integrated nutrient management. Use of 2.5 kg hydrogel ha^?1 resulted in more removal of N; P and K uptakes were higher in 5.0 kg hydrogel ha^?1. Combination of three managements had a consequence of actual soil N loss, but gains in soil P and K after three cropping cycles.     

Root exudation of sugars,amino acids,and organic acids by maize as affected by nitrogen,phosphorus, potassium,and iron deficiency

Root exudates play a major role in the mobilization of sparingly soluble nutrients in the rhizosphere. Since the amount and composition of major metabolites in root exudates from one plant species have not yet been systematically compared under different nutrient deficiencies, relations between exudation patterns and the type of nutrient being deficient remain poorly understood. Comparing root exudates from axenically grown maize plants exposed to N, K, P, or Fe deficiency showed a higher release of glutamate, glucose, ribitol, and citrate from Fe‐deficient plants, while P deficiency stimulated the release of γ‐aminobutyric acid and carbohydrates. Potassium‐starved plants released less sugars, in particular glycerol, ribitol, fructose, and maltose, while under N deficiency lower amounts of amino acids were found in root exudates. Principal‐component analysis revealed a clear separation in the variation of the root‐exudate composition between Fe or P deficiency versus N or K deficiency in the first principal component, which explained 46% of the variation in the data. In addition, a negative correlation was found between the amounts of sugars, organic and amino acids released under deficiency of a certain nutrient and the diffusion coefficient of the respective nutrient in soils. We thus hypothesize that the release of dominant root exudates such as sugars, amino acids, and organic acids by roots may reflect an ancient strategy to cope with limiting nutrient supply.     

黄土丘陵沟壑区自然恢复坡面植物根系的分布特征

采用土钻法研究了黄土丘陵沟壑区自然恢复坡面土壤根系的分布特征及土壤养分含量与土壤水分含量对根系分布的影响。结果表明:根系的分布因坡向、侵蚀带、土层深度、植被类型等的不同而异。阳坡根系总生物量高于半阴坡,但差异不显著;沟谷地根系总生物量及≤1mm根系生物量与沟间地各侵蚀带存在显著性差异;随着土层深度的增加,根系生物量减小;不同植被类型及其盖度对根系生物量有很大影响。不同坡向、各侵蚀带、不同土层中各径级根系生物量的总体趋势是≤1mm根系生物量最大,1～2mm次之,2～3mm和>3mm根系生物量较小,且≤1mm根系生物量与2～3mm和>3mm根系生物量间存在显著差异。根系生物量与土壤养分(除全磷)总体为中度正相关,与土壤水分分布不一致。因此,根系分布不仅与植物自身特性有关,还受土壤环境的影响。     

Transformations and Availability of Iron to Wheat as Influenced by Phosphorus and Manganese Fertilization in a Typic Haplustept Soil

An investigation was conducted using Typic Haplustept, sandy loam soil, to investigate the interactive effects of phosphorus (P) and manganese (Mn) fertilization on native iron (Fe) pools in soil and their availability to wheat (cv. PBW-343) crop. Phosphorus fertilization moved Fe from residual mineral fraction of Fe to manganese oxides (MnOX), organic matter (OM), amorphous (AMPOX), and crystalline (CRYOX) Fe and Al oxide fractions. However, Mn application decreased specifically adsorbed (SAD)–Fe and CRYOX–Fe but increased OM–Fe and mineral fraction of Fe. Available Fe in soil decreased as Olsen P and P:Mn ratio increased in the soil. Higher Olsen P (>60 mg P kg^?1soil) reduced mean Fe uptake by shoot. P content and P:Mn ratio in soil as well as in root and shoot were inversely related to Fe concentration in both the plant parts. The role of soil Fe associated with oxides and organic matter was found most notable in Fe nutrition of wheat.     

Mycorrhizas Mitigate Soil Replant Disease of Peach Through Regulating Root Exudates,Soil Microbial Population,and Soil Aggregate Stability

Soil replant disease is the main bottleneck interfering with tree growth of peach in soils with poor traits. A potted study was conducted to evaluate the effects of inoculation with an arbuscular mycorrhizal fungus (AMF), Acauloapora scrobiculata, on plant growth, mineral nutrients, soil enzyme activities, soil microbial populations, and root exudate compositions of peach (Prunus persica L. Batsch) seedlings grown in replant soil and non-replant soil. After 15 weeks in AMF inoculation, replant soil heavily inhibited root mycorrhizal colonization. In replant soil, AMF inoculation significantly increased shoot biomass and root phosphorus, potassium, calcium, copper, zinc, iron, and boron concentrations. Mycorrhizal peach seedlings showed a higher number of soil bacteria and total microbes but a lower number of soil fungi under replant conditions, as well higher soil urease and acid phosphatase activity and lower soil sucrase and catalase activity. Greater soil aggregate stability was observed in mycorrhiza-inoculated replant soil than in non-mycorrhizal soil due to the increase of water-stable aggregates in 2–4 mm and 1–2 mm size. In addition, a total of 92 substances were identified in root exudates, and the mycorrhizosphere had considerably more root exudate compositions. AMF inoculation had a significantly inhibitive effect on the relative abundance of allelochemical substances, including benzoic acid, benzaldehyde, diisooctyl phthalate, phenols, and sterols, while there was an increase in diphenyl-ethanedione and à-(benzoyloxy)-benzeneacetonitrile in replanted peach. It was concluded that AMF inoculation could partly mitigate soil replant disease of peach through modulating soil microbe balance, improving soil aggregate stability, and changing root exudate compositions.     

Effect of Nitrate/Ammonium Ratios on Growth,Root Morphology and Nutrient Elements Uptake of Watermelon (Citrullus Lanatus) Seedlings

Nitrogen is taken up by most plant species in the form of nitrate and ammonium. The objective of this study was to investigate the effect of different nitrogen forms on the growth of watermelon seedlings. Plants were grown in hydroponic culture with five nitrate (NO₃^?)/ammonium (NH₄⁺) ratios (100/0, 75/25, 50/50, 25/75, 0/100). When the proportion of NH₄⁺ was increased, the leaf number, leaf area, shoot height, net photosynthesis, biomass, and root growth were significantly decreased. Higher concentrations of nitrogen (N) and phosphorus (P) were observed when plants were supplied with mixed NO₃^? and NH₄⁺ compared to NO₃^? or NH₄⁺ alone, whereas the concentrations of potassium (K), calcium (Ca), and magnesium (Mg) were decreased with increasing NH₄⁺. The microelements concentrations were generally increased with more NH₄⁺ added. In addition, plants fed with higher NO₃^?/NH₄⁺ ratios resulted in more minerals accumulation.     

不同复种模式对云南植烟红壤根区有机碳和微生物量碳的影响

建立合理的轮作制是解决烟草种植土壤障碍的有效途径。云南植烟地块,在秋冬季节主要以轮作小麦、紫花苕、豆类及蔬菜等作物为主,在云南曲靖和晋宁烟草种植区,选择了小麦收获后留根茬（20cm左右）翻压后种植烟草（麦-烟）,紫花苕子收获后留根茬（30cm左右）翻压后种植烟草（绿-烟）、豆类（豆-烟）和蔬菜（菜-烟）收获后根茬及秸秆全部移除地外种植烟草的4种轮作模式,研究了不同模式对植烟红壤微生物碳（SMBC）及土壤有机碳（SOC）的影响。结果表明：绿-烟和豆-烟复种模式下,植烟生长期内根区SMBC及SOC均高于麦-烟、菜-烟复种及冬闲地,并且差异达显著或极显著水平;不同复种模式下,SMBC、SOC及SMBC/SOC间呈显著相关性,绿-烟及豆-烟复种模式有利于提高SMBC与SOC含量,延长土壤活性功能,SMBC曲线变化的高峰值均出现在成熟期,其余模式则出现在旺长期;不同模式对提高SMBC与SOC含量影响为：绿-烟〉豆-烟〉麦-烟〉冬闲地〉菜-烟。据此认为土壤SMBC或SMBC/SOC可作为轮作模式影响烟地红壤质量变化的生物学评价指标。     

Survey of Mycorrhizal Colonization in Native,Open-Pollinated,and Introduced Hybrid Maize in Villages of Chiquimula,Guatemala

Replacing native plant types with introduced cultivars may have unexpected cropping system consequences. Native species and introduced cultivars may vary in their ability to form mycorrhizal symbioses with soil fungi and consequently affect phosphorus (P) nutrition. Low-input cropping systems often depend on mycorrhiza for adequate nutrition and growth, while high-input systems minimize the benefit of and need for colonization. Studies in wheat (Triticum aestivum L.) suggest that improving cultivars reduced the ability to form mycorrhiza. This study was conducted at six sites in the province of Chiquimula, Guatemala, to determine the difference in mycorrhizal infection rates between two maize (Zea mays L.) cultivars—‘Cushpeño,’ a native, open-pollinated variety, and ‘HB-83,’ an introduced, improved hybrid. The ‘HB-83’ was colonized at a significantly lower percentage (67%) than was ‘Cushpeño’ (72%; α = 0.0137). A strong negative correlation (r = ?0.953) existed between Mehlich-3 extractable soil P and differences in mycorrhizal colonization rates between the two genotypes. The full impact of lower colonization rates of the introduced hybrid on sustainability of the village agricultural system needs further investigation.     

Diffusive fluxes of phosphorus,potassium and metallic microelements as affected by soil compaction

ABSTRACT

The objective was to evaluate the effects of soil compaction on phosphorus (P), potassium (K), zinc (Zn), copper (Cu), iron (Fe) and manganese (Mn) diffusive fluxes. The experiment consisted of two Oxisols and eight compaction pressures. The soil samples were placed in diffusion chambers, simultaneously with two ion-exchange membranes (anionic and cationic), compressed and incubated for 20 days. The P, K, Zn, Cu, Fe, and Mn diffusive fluxes (PDF, KDF, ZnDF, CuDF, FeDF, and MnDF) were determined. The compaction decreased the PDF in the oxidic-gibbsitic soil, and increased KDF, ZnDF, CuDF, and MnDF, in both soils. There was a higher diffusion of Zn, Cu, and Mn in the kaolinitic than the oxidic-gibbsitic soil. The descending order of cationic-microelement diffusive flux was MnDF > ZnDF ? FeDF > CuDF. Presumably, Fe was mainly diffused as organic complexes with net negative charges, whereas Zn and Mn as free ions and, or, inorganic and organic complexes with positive charges.

Abbreviations: CuDF, cupper diffusive flux; FeDF, iron diffusive flux; KDF, potassium diffusive flux; MnDF, manganese diffusive flux; PDF, phosphorus diffusive flux; ZnDF, zinc diffusive flux; AEM, anion-exchange membrane; CEM, cation-exchange membrane